Raymond Brennan

An Overview of Rapidly Prototyped Piezoelectric Actuators and Grain-Oriented Ceramics

Rapid prototyping (RP) has been used to fabricate a series of piezoelectric actuators, including spiral and tube actuators, to study the actuation mechanism in these geometries, and to obtain enhanced properties. PZT spiral actuators showed large displacement in mm range, and moderate blocking force. Unimorph spirals (PZT/metal shim) and dual-material (piezoelectric/electrostrictive) PMN-PT spirals were also prototyped and characterized. Tube actuators with inward and outward wall curvature showed slight improvement in axial and radial displacements compared to conventional straight-walled tube actuators. In order to improve the performance of ceramic actuators with polycrystalline microstructures, grain-oriented ceramics of bismuth titanate, lead metaniobate, and PMN-PT were investigated. Texturing was achieved by incorporating anisometric seeds into RP feedstock, aligning them during fabrication, and growing the seeds (templates) at elevated temperatures. Synthesis of anisometric seeds and pertinent processing conditions of the textured ceramics are presented. The feasibility of making net shape single crystal components was also explored. Single crystals of 0.65PMN-0.35PT were grown in FDC components using embedded (111) and (110) SrTiO3 seeds at 1250°C.

Fabrication of electroceramic components by layered Manufacturing (LM)

Layered Manufacturing (LM) has been developed and utilized to provide a cost-effective route to rapidly turn new designs into net-shape components. In LM, components are built layer-by-layer via a computer-controlled dispensing system, directly from a CAD file. Fused Deposition of Ceramics (FDC), which is used for single material fabrication, and Fused Deposition of Multi-Materials (FDMM), which is used to fabricate prototypes composed of up to four materials, are two examples of techniques employed to produce a variety of electroceramic components at Rutgers University. Novel piezoelectric and electrostrictive actuators and sensors with single and multi-materials have been prototyped via LM such as spiral and telescoping actuators, volume fraction gradient composites, and oriented structures. The concept of Templated Grain Growth (TGG) has been combined with LM to initiate the fabrication of net-shape grain-oriented and single crystal components.

Ultrasonic NDE of silicon carbide lightweight systems

Silicon carbide (SiC) high energy mirrors from M-Cubed, Schafer Corp, Poco and Trex Inc. were investigated using nondestructive ultrasound C-scan imaging. Reflected signal amplitude variations from the top surface of the SiC mirrors were imaged to locate surface and subsurface inhomogeneities. Where possible, the bottom surface reflected signal amplitude and material velocity were mapped to evaluate bulk properties. Elastic property mapping was also performed on a dense SiC mirror sample to look for regional variations in Poissons ratio, Youngs modulus, shear modulus, and bulk modulus. These ultrasound techniques were successfully utilized for detection of subsurface inhomogeneities in the SiC mirror samples.

Templated grain growth (TGG) of PMN-PT textured components using SrTiO/sub 3/ templates

Tapes of PMN-PT containing 5 to 10 volume % of SrTiO/sub 3/ seeds were cast and subjected to heat treatments of 1250/spl deg/C in either air or oxygen atmospheres for 10 hours in order to texture the samples and enhance the (h00) peaks of PMN-PT. Lead-based additives such as lead oxide (PbO) and lead carbonate (PbCO/sub 3/) were introduced to create a liquid phase during heat treatment of the samples. The effects of sintering atmosphere, sintering time, and addition of lead-based additives were studied to determine which factors resulted in the highest degree of texturing. SEM studies revealed that the grown PMN-PT regions from the SrTiO/sub 3/ seeds were approximately 40-60 /spl mu/m in length after proper heat treatment. XRD studies showed an enhancement in the (100) and [200] crystallographic orientations of PMN-PT. Calculated Lotgering factor (f) values indicated that the samples fabricated with 1 wt.% PbO at 1250/spl deg/C for 10 hours in an oxygen atmosphere were textured up to /spl sim/50%.

Layered manufacturing for prototyping of novel transducers

Layered Manufacturing (LM) technology has been implemented to prototype novel piezoelectric ceramics and composites for sensor and actuator applications. Piezoelectric actuators in the form of tubes, telescoping, spirals and ovals have been manufactured. Among actuators, spirals have shown giant tangential displacements up to several millimeters at moderate electric field. Multimaterials actuators have also been prototyped to study field-induced strain in these structures. In addition to actuators, piezocomposite sensors with oriented 2-2 and 3-3 composites were prototyped, in which the ceramic phase was oriented with respect to the poling direction. Various piezoelectric properties were measured and calculated. The hydrostatic figure of merit at an orientation angle of 45 degrees was significantly (50-80 times) larger than those of the conventional piezocomposites. Recently, we have fabricated net shape grain-oriented/single crystal components by integration of LM and Templatcd Grain Growth techniques. Grain oriented PMN-PT, bismuth titanate, and lead niobate components were also made using LM feedstock containing small amounts of platelet or needle-like seeds, resulting in improved piezoelectric properties.

Growth of net-shape PMN-PT single crystal components by fused deposition of ceramics (FDC) and templated grain growth (TGG) techniques

The net-shape capabilities of Fused Deposition of Ceramics (FDC) and the cost efficient growth technique of templated grain growth (TGG) have been combined to fabricate single crystal Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/ (PMN-PT) components. PMN-PT (65/35) filament containing excess lead oxide (PbO) was used to fabricate a matrix layer-by-layer via FDC. SrTiO/sub 3/ (111) and (110) single crystals were embedded into the matrix. After heat treatment of 1250/spl deg/C for 10 hours, the growth was approximately 2.5 mm from the SrTiO/sub 3/ (111) single crystal to the tip of the grown area. The same process was used to grow (110) PMN-PT single crystals as well. X-ray diffraction and x-ray mapping studies have shown that the grown crystals closely match the PMN-PT (65/35) composition, and are oriented in the SrTiO/sub 3/ single crystal direction. As compared to matrix samples sintered under the same conditions, the d/sub 33/ value improved from 390 to 600 pC/N, dielectric constant from 2650 to /spl sim/4500, and the loss tangent from 0.48% to 0.33% for (111) grown crystals. The (110) grown crystal values were improved to d/sub 33/ = 900 pC/N and K /spl sim/ 4450. These techniques are being used to grow net-shape single crystal components such as 2-2 composites and spiral actuators.